S174: HIGH LEVEL OF CIRCULATING TUMOUR DNA AT DIAGNOSIS CORRELATES WITH DISEASE SPREADING AND DEFINES MULTIPLE MYELOMA PATIENTS WITH POOR PROGNOSIS
Authors: M. Martello, A. Poletti, D. Bezzi, E. Borsi, B. Taurisano, V. Solli, S. Armuzzi, I. Vigliotta, G. Mazzocchetti, I. Pistis, L. Pantani, S. Rocchi, K. Mancuso, P. Tacchetti, I. Rizzello, M. Cavo, E. Zamagni, C. Nanni, C. Terragna
Journal: HemaSphere (2022)

Background: Multiple Myeloma (MM) is a plasma cell (PC) disorder characterized by the presence of skeletal involvement at the time of diagnosis, as detected by MRI and/or FDG PET/CT, in most of the patients. The patchy nature of the disease is probably related to the ability of fitter clones to spread into peripheral blood reaching distant sites, where favourable microenvironment conditions might promote clones’ seeding. Recently, cell-free DNA (cfDNA) has been proven to resume the heterogeneity of spatially distributed clones. However, it has to be determined to which extent cfDNA correlates with disease distribution and its possible implications with patients’ outcome. Moreover, the potential of cfDNA to track the evolutionary dynamics and the heterogeneity of MM, possibly anticipating the emergence of therapy resistant residual cells, remains to be confirmed. Aims: Aim of this study is to quantitatively and qualitatively evaluate cfDNA at diagnosis and during follow-up in correlation with imaging data to possibly define the integration of this approach with molecular bone marrow (BM) and whole-body residual disease assessment. Methods: A total of 88 newly diagnosed MM patients were screened at baseline with 18F-FDG PET/CT, and molecularly assessed by Ultra Low Pass-Whole Genome Sequencing (ULP-WGS). In a subgroup of 22 patients, cfDNA was monitored monthly, whereas PET/CT was reassessed after induction therapy to evaluate metabolic tumor response. For each pts, ULP-WGS was used to characterize both the neoplastic PC clone(s) in the BM (gDNA) and the cfDNA from peripheral blood. Data were analysed by ichorCNA and Clonality R packages. Results: At diagnosis, the cfDNA tumor fraction (TF) was significantly lower as compared to gDNA TF [median (M) TF: 4.4 vs. 59.7%, respectively]. Nevertheless, high cfDNA TF levels (> 4.4% cfDNA TF values; range: 4.4-84.3%) correlated with high gDNA TF levels (>65.7% gDNA TF values; range: 65.7-96.7%). This observation was further confirmed by a significant correlation between cfDNA TF and the percentage of BM CD138/CD38 positive plasma cells (r=0.47; p<.0001). Interestingly, patients with high cfDNA TF at baseline were more likely to present with extramedullary disease (EMD) and a higher number of focal lesions, and also featured a more active tumour metabolism, as compared to pts with low TF (EMD 4/44=9% vs. 1/44=2.3%, p=ns; M n. PET lesions: 1.7 vs. 2.5, p= 0.003; SUVmax: 5.2 vs. 9.6, p = 0.01). Despite an overall concordance between cfDNA and BM genomic profiles (80/88=90.9%), those patients with high cfDNA TF showed more frequently evidence of spatial heterogeneity, as highlighted by a substantial divergence of copy number alterations profiles between cfDNA and gDNA (7/8=87.5% of pts with divergent profiles). Finally, high cfDNA TF at diagnosis predicted for poorer prognosis as compared with low cfDNA TF (PFS at 20 months: 67% vs. 86%, p=0.05; OS at 20 months: 90% vs. 100%, p=0.04). Interestingly, after bortezomib-based induction therapy, imaging data and cfDNA TF levels were concordant; notably, in 4/10 (40%) patients with median SUVmax 5.8 and >2 PET lesions, cfDNA TF was still detectable (>1% TF), thus corroborating a possible role for cfDNA in monitoring response to therapy. Summary/Conclusion: In conclusion, patients with high cfDNA TF displayed imaging data that overall suggested a higher propensity to a metastatic spread of the disease, which finally correlated with poorer prognosis. Future studies will be addressed to exploit the use of cfDNA in disease monitoring. Acknowledgements: AIRC IG2019, AIL BOLOGNA ODV